. >>> ktvu health and science center live where people not only have to deal with heat but another potential health threat. >> reporter: first of all the, as bill said going to get to 100s. health officials are telling everybody keep the water bottle handy and hat on your head to avoid the risks of heat stress. >> at 3:00 p.m., officially 91 degrees. >> shorts, flip flops, lay out in the sun and go swimming. i love it. >> it was 93 but people said it felt hotter. >> i have a cat and a kid. we have to run ac. >> the technician tested this algae filled standing water and found a sudden explosion of mosquito larva. >> it adds up to something we need to be concerned about. >> mosquito control told me they found the first positive west nile bird of the season. plus a troubling mosquito species new carrying yellow fever. >> they can have fatal diseases. like all mosquitoes, they need water. >> mosquito nt